The authors declare they do not have any affiliation with industries or organizations with a financial interest, direct or indirect, that may affect the conduct or reporting of the work submitted.
Biological functions and therapeutic use of erythropoiesis-stimulating agents: perplexities and perspectives
Article first published online: 17 APR 2009
© 2009 Blackwell Publishing Ltd
British Journal of Haematology
Volume 146, Issue 2, pages 127–141, July 2009
How to Cite
Merchionne, F. and Dammacco, F. (2009), Biological functions and therapeutic use of erythropoiesis-stimulating agents: perplexities and perspectives. British Journal of Haematology, 146: 127–141. doi: 10.1111/j.1365-2141.2009.07702.x
- Issue published online: 1 JUL 2009
- Article first published online: 17 APR 2009
- erythropoietin receptor;
Randomized clinical studies, carried out in patients with haematological malignancies and with solid tumours, have consistently demonstrated that treatment with recombinant human erythropoietin (Epo) increases haemoglobin levels, reduces blood transfusion requirements, and improves the quality of life. In addition, identification of erythropoietin receptor (EpoR) expression on many types of non-erythroid and cancer cells has spurred an interest in the extra-haematological activities of Epo itself and other erythropoiesis-stimulating agents (ESAs). Epo and its derivatives have emerged as major tissue-protective cytokines in ischaemic and degenerative damage of cardiovascular, neurological and renal diseases, while their angiogenetic and immunomodulatory properties indicate that their therapeutic potential may extend well beyond erythropoiesis alone. Both preclinical and clinical data, however, have suggested that they may contribute to tumour progression and prejudice survival when administered to anaemic cancer patients, though the results are equivocal and the assumed mechanisms by which tumour growth could be promoted are not fully understood. While these findings offer new perspectives, they nonetheless demand caution in the employment of ESAs. Further, well-designed experimental and clinical studies are warranted.
Recombinant human erythropoietin (rHuEpo), also called epoetin, entered clinical practice in the late 1980s for the treatment of anaemia associated with renal failure and was later employed for the management of chemotherapy- or radiotherapy-induced anaemia in cancer patients. Randomized clinical studies have consistently shown that it increases haemoglobin (Hb) levels, reduces red blood cell (RBC) transfusion requirements, and improves the quality of life (Spivak, 1994; Dammacco et al, 1998, 2001; Littlewood et al, 2001; Boogaerts et al, 2003; Hedenus et al, 2003; Osterborg et al, 2005; Witzig et al, 2005).
Three erythropoiesis-stimulating agents (ESAs) are currently used in clinical practice, namely epoetin alfa (Procrit®; Ortho Biotech, Bridgewater, NJ, USA; Epogen®; Amgen, Thousand Oaks, CA, USA; Eprex®; Janssen-Cilag, Cologno Monzese, Milan, Italy), epoetin beta (NeoRecormon®; F. Hoffmann-La Roche, Basel, Switzerland) and darbepoetin alfa (Aranesp®; Amgen), which is a hyperglycosylated Epo analogue with an extended serum half-life compared to rHuEpo. These agents are administered subcutaneously and have comparable profiles of effectiveness and safety. More recently, a third-generation molecule, namely continuous erythropoietin receptor activator (CERA: Mircera®; Roche), with a longer half-life than either epoetin or darbepoetin alfa, has been proposed for the management of chronic kidney disease and is currently under experimental and clinical investigation (Macdougall, 2005). Several studies, motivated by the growing evidence of erythropoietin receptor (EpoR) expression on non-erythroid cells (Arcasoy, 2008) and on various types of malignant tumour cells (Hardee et al, 2006), have also shown that ESAs are endowed with biological and tissue-protective effects. At the same time, however, the possibility that they may modulate cancer cell growth, favour tumour progression, and reduce overall survival has equally been put forward as a cause for concern.
There is thus an obvious need to redefine the role and use of ESAs through revision of current guidelines in clinical practice in order to achieve the maximum benefit, and reduce the risks that may be associated with their administration. In March 2008 members of the Oncology Drug Advisory Committee (ODAC) of the U.S. Food and Drug Administration convened to discuss and disseminate the cumulative data on the safety of ESAs in cancer patients, to indicate further restrictions and to recommend additional double-blind, placebo-controlled studies with primary endpoints of overall survival. Similar actions have been pursued by other regulatory agencies worldwide. The UK Medicines and Healthcare products Regulatory Agency (MHRA), for example, has included rHuEpo in the list of drugs under intensive surveillance.
This article reviews the biological effects of ESAs, their efficacy and tolerability, and the results of preclinical and clinical investigations of their influence on tumour cell growth and the survival of anaemic cancer patients. Current views with regard to the expression of EpoR in non-erythroid cells and the non-haematopoietic functions related to the Epo-EpoR signalling are also discussed.
ESAs and haematological functions
Erythropoietin (Epo) is a 30·4 kDa glycoprotein hormone that regulates erythropoiesis and is normally secreted by the adult kidney and the fetal liver. Its gene expression is mainly affected by decreased tissue oxygen tension via activation of the transcription factor HIF-1 (hypoxia inducible factor-1), which binds a site in the 3′ enhancer of the gene, and increased mRNA stability (Ebert & Bunn, 1999; Fandrey, 2004). Physiologically, Epo prevents apoptosis and stimulates the proliferation and terminal differentiation of cells committed to the erythroid lineage by binding to a specific receptor (EpoR) expressed on their surface. EpoR is a 55 kDa protein that is modified by glycosylation and phosphorylation to 72–78 kDa. It is a dimeric receptor and belongs to the cytokine receptor family; its structure is characterized by conserved motifs in the extracellular domain (four conserved cysteines, a group of aromatic residues and a WSXWS motif), a transmembrane preformed dimer that changes conformation upon binding of its ligand, and an intracellular domain required for signalling cascades (Fig 1).
Epo/EpoR-induced signals result in the autophosphorylation of Janus kinase JAK2, a member of the family of tyrosine kinases. It is constitutively associated with EpoR homodimers and mediates the rapid phosphorylation of eight conserved tyrosine residues (PY) of cytoplasmic EpoR that act as fastening sites for various signal transduction proteins (Tilbrook & Klinken, 1999). One of these, transcription factor STAT-5 (signal transducer and activator of transcription-5), is recruited to the receptor complex. Following activation via PY 343, it dimerises and moves to the nucleus where it promotes the transcription of target genes, such as OSM and PIM1, that enhance erythroblast survival, the signalling inhibitor CIS/cytokine-inducible SH2-protein and SOCS (members of suppressor of cytokine signalling family), and Bcl-x (an anti-apoptotic protein). Some of these PY sites are negative regulatory domains of EpoR insofar as they recruit molecules that inactivate signalling, such as tyrosine phosphatase SHIP-1, which dephosphorylates PY 429 and JAK-2 (Klingmuller et al, 1995), or CIS3/SOCS-3 which binds PY 401 (Sasaki et al, 2000) and another EpoR tyrosine motif with PY 429 and PY 431, and interferes with the activation of JAK2/STAT-5 (Hortner et al, 2002).
Other SH2-containing proteins, namely PI3K (phosphatidylinositol 3-kinase), Grb2/Shc and PLCγ (phospholipase C-γ), are activated in the Epo response (Bouscary et al, 2003). In addition, activation of the Ras/MAP kinase pathway is associated with EpoR and plays an important role in Epo-dependent cell proliferation and the regulation of gene expression (Klingmuller, 1997). Lastly, an experimental study has demonstrated Epo-mediated activation of the transcription factor nuclear factor (NF)-κB signalling pathway without involvement of JAK2 (Bittorf et al, 2001).
Menon et al (2006) have shown that the PY343-STAT-5 pathway has a selective and crucial role in the regulation of erythropoiesis during both acute haemolytic anaemia and anaemia associated with chemotherapy and bone marrow transplantation. This emphasizes the difference in level of EpoR signalling between steady-state and stress-induced erythropoiesis, and demonstrates that in STAT-5a,b−/− mice this pathway promotes oncostatin-M, but not Bcl-x expression, both of which enhance the survival of erythroid progenitors.
ESAs and extra-haematological functions
Many non-erythroid cell types are known to express EpoR: vascular endothelial cells, astrocytes and neurons, myoblasts, smooth muscle cells, cardiac myocytes, and retina, kidney and mammary epithelial cells (Arcasoy, 2008). Its specific function in most of these cell types is still poorly understood, though some tissue-protective biological functions associated with its activation in non-haematopoietic cells by exogenous or endogenous Epo have been observed. In vitro and animal studies have shown that these functions are mediated by a surface receptor that is structurally different from the receptor that controls erythropoiesis and characterized by interaction with βcR subunit of the interleukin-3 receptor (Brines et al, 2004). The precise role of this interaction has not been elucidated. Even so, these results support the view that the Epo-EpoR signalling activation mechanisms associated with erythropoiesis and tissue-protective functions of Epo are not the same. Although the βcR subunit was initially claimed to be involved in erythroid progenitor signalling (Shikama et al, 1996), a recent study on differentiated neuroblastoma SH-SY5Y and pheochromocytoma PC-12 cells indicated that, in these types of cells, the cytoprotective anti-apoptotic effect is mediated by the normal homodimer EpoR in a manner similar to haematopoietic cells (Um et al, 2007).
The effects of Epo on vascular endothelial cells and in the regulation of physiological and pathological angiogenesis have been extensively demonstrated. In vitro, the Epo-EpoR system promotes the proliferation, migration and differentiation of normal endothelial cells into vascular tubes and hence the formation of new blood vessels (Carlini et al, 1995; Haller et al, 1996), whereas in vivo it stimulates chick embryo development (Ribatti et al, 1999), wound healing (Haroon et al, 2003), and oestrogen-dependent cyclical angiogenesis in the uterus (Yasuda et al, 1998). Its involvement in the pathological angiogenesis of proliferative diabetic retinopathy (Watanabe et al, 2005) and tumours (Hardee et al, 2006) has also been demonstrated, even though its role in cancer progression is by no means certain.
It is noteworthy that tissue neovascularization has emerged as a source of Epo’s cardioprotective effects in animal models of myocardial infarction, probably through its mobilization of endothelial progenitor cells from bone marrow into the blood (Heeschen et al, 2003; van der Meer et al, 2005; Silverberg et al, 2005). Administration of Epo before or up to 12 h after coronary artery ligation reduced cardiac myocyte apoptosis and overall impairment of cardiac function (Calvillo et al, 2003; Moon et al, 2005). A pilot study has since been conducted to examine the effect of darbepoetin alfa in non-anaemic patients with acute myocardial infarction. A single i.v. 300 μg dose was both safe and well tolerated, whereas the left ventricular ejection fraction at 4 months was similar to that of patients who did not receive additional medication before primary coronary surgery. Further clinical trials are evidently required to establish the efficacy of Epo in patients with cardiac ischaemia (Lipsic et al, 2006). Epo is also protective against cardiotoxicity due to chemotherapeutic agents, such as doxorubicin (Hamed et al, 2006). These results indicate that Epo-mediated cardioprotection is mainly dependent on the signalling PI3K-AKT pathway (Tramontano et al, 2003), though the phosphorylation of other proteins, such as MAP kinases ERK-1/2, has been demonstrated (Fu & Arcasoy, 2007).
The biological and tissue-protective effects of Epo have also been widely investigated in the nervous system and kidney. It has indeed been shown in vitro that rHuEpo protects embryonal, hippocampal and cortical neuronal cells presenting EpoR from cell death induced by neurotoxic molecules and hypoxia (Liu et al, 2006; Won et al, 2007). This effect has been associated with increased hypoxia-induced EpoR expression and sensitivity to Epo (Yu et al, 2002).
More recent in vivo studies have reported that Epo produced in the mouse central nervous system during chronic hypoxia protects the brain. This protection, in fact, is abolished by infusion of a soluble form of EpoR and neuronal degeneration ensues (Sakanaka et al, 1998). Other studies of rats as experimental models of stroke have indicated that systemic administration of rHuEpo before or up to 6 h after ischaemic brain injury reduces the extent of cerebral infarction after crossing the blood-brain barrier (Brines & Cerami, 2005), as well as in humans, whose functional outcome is improved when it is administered within 8 h after stroke (Ehrenreich et al, 2002).
The neuroprotective effect of Epo in the peripheral nervous system takes the form of reduction of the axonal degeneration typical of peripheral neuropathies (Toth et al, 2008), while experimental studies have confirmed its positive role in the prevention and treatment of both diabetic neuropathy and polyneuropathy induced by chemotherapeutic agents, such as cisplatin and paclitaxel (Bianchi et al, 2004, 2006; Melli et al, 2006).
As in the case of haematopoietic cells, in neuroprotection, many signalling pathways, including JAK-2/STAT-5, ERK-1/-2 and PI3K/AKT, are simultaneously activated after endogenous Epo stimulation in the ischaemic brain, particularly in mediating the anti-apoptotic effect (Kilic et al, 2005). However, the intracellular signalling pathway seems to involve JAK2 and the nuclear transcription factor NF-κB, which triggers NF-κB-dependent transcription of neuroprotective genes and, probably, inhibitory proteins of apoptosis (Digicaylioglu & Lipton, 2001).
Protection of the kidney by Epo has not been definitely established. In vitro studies have shown its direct effect on proliferation and cell death in proximal tubular epithelial cells, while in experimental models of acute renal failure it reduces tubular cell death and hence the dysfunction induced by ischaemia reperfusion injury (Sharples & Yaqoob, 2006). Benefits of Epo have been reported in animal models of systemic shock and nephrotoxicity induced by cisplatin and ciclosporin (Bagnis et al, 2001; Lee et al, 2005). In contrast, in a model of radiation-induced kidney dysfunction, protective administration of Epo was disappointing because it was associated with deterioration of renal function (Andratschke et al, 2006).
In the last few years, the effect of Epo on immunity has emerged in reports of tumour regression in murine myeloma models as the result of a T CD8+ cell-mediated immune response (Mittelman et al, 2001). Other studies by the same authors have indicated that Epo may be associated with prolonged survival in patients with advanced multiple myeloma (Mittelman et al, 2004). It is suggested that this anti-myeloma effect could be related to immune system modulation, given that Epo induces normalization of CD4/CD8 cell ratio, enhances T-cell phytohaemagglutinin-mediated activation and potential proliferation, reduces the percentage of CD8+ T cells expressing the inhibitory molecule CTLA-4 (cytotoxic T lymphocyte-associated 4) and increases CD8+ T cells expressing the costimulatory CD28 (Prutchi-Sagiv et al, 2006). Some of these results have also been confirmed by other workers (Baz et al, 2007).
Epo and EpoR in tumours: the preclinical experience
Many experimental studies have shown Epo-R expression in a variety of tumour cell lines. EPO mRNA transcripts and proteins, also induced by hypoxia, were detected in the cytoplasm of hepatocarcinoma cells, melanoma, breast, colon, pancreas, gastric, ovarian, uterine, renal, bladder, prostate, non-small-cell lung, head and neck carcinoma, and B-cell haematological malignancies (Hardee et al, 2006; Kokhaei et al, 2007). However, there is at present a considerable controversy on the techniques used for EpoR detection, such as Western blot, immunoprecipitation and immunohistochemical analysis, that are unable to distinguish EpoR expression on cell surface (where it is normally activated by Epo) from intracellular location. In addition, expression (or RNA) of a protein does not necessarily mean that it is functional. This point has been clearly addressed in the pivotal editorial of Longmore (2007). Moreover, most studies have identified EpoR by using non-specific commercially available anti-EpoR antibodies, which can also bind multiple proteins with different molecular size (Elliott et al, 2006). Similarly, sensitive reverse-transcription polymerase chain reaction (RT-PCR) analysis has been shown to identify EPOR mRNA transcript, but this evidence does not necessarily mean its translation into functional EpoR expression. Recently, two reports have evaluated EpoR cell surface expression in tumour cells through EpoR binding studies with radiolabeled Epo (LaMontagne et al, 2006; Um et al, 2007); the first report emphasized the absence of measurable Epo-specific binding activity and the second, a very low number (fewer than 50 molecules/cell) of high affinity surface binding sites compared to erythroid cells. Taken together, these findings suggested that EpoR protein can be synthesized but not carried to the cell surface, probably because of the lack of accessory trafficking factors (Sinclair et al, 2008).
Another essential issue is whether EpoR is able to elicit a biological response of tumour cells to binding with Epo, through the transduction of EpoR-mediated signalling pathways. Numerous in vitro studies have shown Epo-induced activation of the major EpoR signalling cascades in various cancer cell lines (Lai et al, 2005; Lester et al, 2005; Mohyeldin et al, 2005; Kumar et al, 2006; Um & Lodish, 2006; Hamadmad & Hohl, 2008; Jeong et al, 2008), associated with increased tumour cell migration, invasion and apoptosis inhibition, while upregulation of Epo and EpoR expression during hypoxia suggested the establishment of a supportive autocrine loop (Lester et al, 2005; Mohyeldin et al, 2005). Nevertheless, most studies failed to show tumour cell proliferation following stimulation by Epo and only a few papers have reported a limited increase in vitro in the proliferation of breast, renal and prostate carcinoma cells (Westenfelder & Baranowski, 2000; Acs et al, 2001; Feldman et al, 2006), generally using supra-physiological doses of Epo. However, Dunlop et al (2006, 2007) reported the activation of Epo/EpoR signalling in non-small-cell lung carcinoma at pharmacological concentrations of Epo, even if it was not associated with a growth promoting effect on tumour cells. In addition, it has been more recently shown that expression of a constitutively active EpoR variant in breast cancer cells results in their increased proliferation and migration by activation of the ERK- and SAPK/JNK-dependent pathways, but not JAK-2/STAT-5 axis (Fu et al, 2009), suggesting that EpoR over-expression and activation could favour tumour progression.
Enhanced angiogenesis could also promote tumour growth. rHuEpo stimulates the proliferation and migration of endothelial cells, induces their angiogenic phenotype, increases their metalloproteinase (MMP)-2 secretion, inhibits their apoptosis, and is angiogenic in vivo in the chick embryo chorioallantoic membrane in the same way as fibroblast growth factor-2 (Ribatti et al, 1999). These data point to the existence of an autocrine and paracrine circuit that influences a tumours’ biological behaviour. In addition, blockade of Epo signalling in animal models by antibody to Epo or EpoR antagonists inhibits angiogenesis and survival of tumour cells, and leads to the destruction of tumour masses (Yasuda et al, 2001, 2003). These results have since been confirmed by Hardee et al (2007) in an angiogenic model of fluorescence-labelled mammary carcinoma cells implanted in dorsal skin-fold window chambers in mice. Blockade of the Epo-EpoR system proved to be an effective anti-tumour strategy. This study, however, is in contrast with the previous observation by the same authors of the absence of angiogenic and direct growth promoting effects in rats transplanted with rodent and human tumour cells, and treated with a therapeutic dose of Epo (Hardee et al, 2005).
A closely related question is whether rHuEpo increases sensitivity to radiotherapy or chemotherapy. Experimental studies in rats transplanted with sarcoma or glioblastoma and treated with Epo prior to radiation therapy to prevent anaemia have revealed higher radio sensitivity and delayed tumour growth as compared with anaemic rats, but shorter than non-anaemic animals (Thews et al, 1998; Stuben et al, 2001). In other studies, however, correction of anaemia up to an increased haematocrit has resulted in a lack of radiosensitivity, probably because of enhanced blood viscosity and hence decreased tumour perfusion (Joiner et al, 1993).
The effect of Epo on the response to chemotherapeutic agents has also been investigated, with conflicting results. Inhibition of cisplatin-induced apoptosis was reported by three studies on human cervical cancer, glioblastoma and renal carcinoma cells respectively, treated with rHuEPO at doses from 25 to 200 U/ml (Acs et al, 2003; Belenkov et al, 2004; Li et al, 2007). In contrast, in a study using a lower dose of Epo (10 U/ml) in various cancer cell lines expressing low levels of EpoR, no effect was shown on bcl-2 expression and no modification in responsiveness to subsequent treatment with cisplatin (Liu et al, 2004). However, studies in severe combined immunodeficient (SCID) mice bearing human ovarian cancer cells have provided evidence of a correlation between Epo administration and sensitivity to cisplatin, associated with a 25–35% increase of haematocrit (Silver & Piver, 1999). In other animal models it was demonstrated that correction of anaemia with ESAs during treatment with cyclophosphamide enhances sensitivity to this drug by improving tumour tissue oxygenation and thus delaying cancer growth, compared to the anaemic controls (Thews et al, 2001).
ESAs in the treatment of anaemia in cancer patients
Anaemia is a frequent complication of cancer. It may be its direct consequence or the outcome of chemotherapy treatment, and adversely affects the overall quality of life (Ludwig et al, 2004). It is also a negative prognostic factor because anaemic patients with lung, cervical, prostate, head and neck cancer, multiple myeloma and lymphoma have a shorter survival and a higher relapse rate than non-anaemic patients at the same disease stage (Caro et al, 2001). Correction of anaemia has thus become a primary goal of disease management, especially since the maintenance of adequate Hb levels allows the establishment of an optimal chemotherapy dose and a timely therapeutic programme. Moreover, in patients undergoing radiation therapy for cervical and head and neck cancer, the increase of Hb levels within the normal range may improve intra-tumoural hypoxia, and then enhance radiosensitivity, provide a better local disease control and possibly result in prolonged survival (Dunst, 2001; Shasha, 2001; Harrison et al, 2002). In respect, the advent of epoetin has been of crucial importance in the oncology setting, owing to its improvement of the quality of life, maintenance of the Hb concentration, and reduction of the need for RBC transfusions.
Several placebo-controlled, randomized studies have clearly illustrated these therapeutic benefits in various types of cancer (Vansteenkiste et al, 2002; Chang et al, 2005; Grote et al, 2005; Savonije et al, 2005; Razzouk et al, 2006; Wilkinson et al, 2006; Pirker et al, 2008; Strauss et al, 2008). The most recent studies in patients with solid tumours and haematological malignancies are summarized in Tables I and II. They have consistently demonstrated a significant increase in Hb concentration and a significant improvement of the quality of life compared to the placebo group. The occurrence of side effects, including thromboembolic events, was similar to that of the placebo group, and there were no significant differences in the median overall survival, time to progression and overall mortality.
|No. of patients||Malignancy||Treatment||ESA||Dose||Hb baseline/Hb stopping value (g/l)||Results||Reference|
|Increased mean Hb (g/l)||Transfusion requirement||Improvement in QoL||Median survival|
|145||Multiple myeloma||Chemotherapy||Epoetin alfa versus placebo||150–300 i/u kg−1 × 3 weekly for 12 weeks||<110/140||18 vs. 0·0; P = 0·001||28% vs. 47%; P = 0·017||P ≤ 0·05||–||Dammacco et al (2001)|
|375||Solid or nonmyeloid haematological malignancies||Nonplatinum chemotherapy||Epoetin alfa versus placebo||150–300 i/u kg−1 × 3 weekly for 28 weeks||≤105 or >105 ≤120/150||22 vs. 5·0; P < 0·001||24·7 vs. 39·5%; P = 0·0057||P ≤ 0·048||At 12 months 60% vs. 49%; P = 0·13||Littlewood et al (2001)|
|344||Lymphoproliferative malignancies||Chemotherapy||Darbepoetin alfa versus placebo||2·25–4·5 μg/kg per weekly for 12 weeks||≤110/140 (women) 150 (men)||26·6 vs. 6·9; P < 0·001||31% vs. 48%; P < 0·001||P = 0·032||–||Hedenus et al (2003)|
|262||Lymphoid and solid tumours||Chemotherapy||Epoetin beta versus standard care||150–300 i/u kg−1 × 3 per weekly for 12 weeks||≤110/140||21 vs. 9·0; P < 0·001||22% vs. 43%; P < 0·001||P < 0·05–0·076||–||Boogaerts et al (2003)|
|343||Lymphoproliferative malignancies||Chemotherapy||Epoetin beta versus placebo||150 i/u kg−1 × 3 weekly for 16 weeks||<100/not reported||67% vs. 27%*; P < 0·0001||–||P < 0·05||17·4 vs. 18 months (HR 1·04, 95% CI: 0·80–1·36)||Osterborg et al (2005)|
|344||All types of cancer||Chemotherapy||Epoetin alfa versus placebo||40 000–60 000 i/u weekly for 16 weeks||<115 (males) <105 (females)/150||28 vs. 9·0; P < 0·0001||25% vs. 40%; P = 0·005||P = 0·18||10·4 vs. 11·2 months; P = 0·53||Witzig et al (2005)|
|224||Non-myeloid malignancies||Chemotherapy||Epoetin alfa versus placebo||600–900 i/u kg−1 per weekly for 16 weeks||<105 (5–12 years) <110 (girls >12 years) <120 (boys >12 years/140–150||13 vs. 10; P = 0·002||24% vs. 45·2%; P = 0·002†||–||–||Razzouk et al (2006)|
|No of patients||Malignancy||Treatment||ESA||Dose||Hb baseline/Hb stopping value (g/l)||Results||Reference|
|Increased mean Hb (g/l)||Transfusion requirement||Improvement in QoL||Median survival|
|320||Lung cancer||Platinum based chemotherapy||Darbepoetin alfa versus placebo||2·25–4·5 μg/kg per weekly for 12 weeks||≤110/ 140 (women) 150 (men)||66% vs. 24%*; P < 0·001||27% vs. 52%; P < 0·001||P = 0·019–0·052||22 vs. 20 weeks†; 46 vs. 34 weeks; P not reported||Vansteenkiste et al (2002)|
|316||Solid tumours||Platinum-based chemotherapy||Epoetin alfa versus supportive care||10 000–20 000i/u × 3 weekly for 4 weeks||≤120/140||76% vs. 45%*; P < 0·001||36% vs. 65%; P < 0·001||P ≤ 0·05||11 vs. 12 months; P = 0·39||Savonije et al (2005)|
|354||Breast cancer||Chemotherapy||Epoetin alfa versus standard care||40 000–60 000i/u weekly for 16 weeks||≤120/140||65·7% vs. 6·3‡; P < 0·0001||8·6% vs. 22·9%; P < 0·0001||P < 0·001||–||Chang et al (2005)|
|224||Small-cell lung cancer||Chemotherapy||Epoetin alfa versus placebo||150 u/kg × 3 weekly§||≤145/160||−2·0 vs. −29; P not reported||24% vs. 37%; (HR = 0·597; 95% CI = 0·365–0·977)||–||10·5 vs. 10·4 months; P = 0·264||Grote et al (2005)|
|182||Ovarian cancer||Platinum-based chemotherapy||Epoetin alfa versus standard treatment||10 000–20 000i/u × 3 per weekly for 28 weeks||≤120/140||16 vs. 3·0; P < 0·001||7·9% vs. 30·5%; P < 0·001||P = 0·054–0·118||11% vs. 2%¶; P = 0·425||Wilkinson et al (2006)|
|74||Cervical cancer||Radio-chemotherapy||Epoetin beta versus standard care||30 000–60 000 i/u per weekly for 12 weeks||<120/150||13 vs. −7·0; P < 0·0001||26·5% vs. 30%; P not reported||–||20·6% vs. 3%¶; P = 0·1223·5% vs. 12·5%**; P = 0·22||Strauss et al (2008)|
|600||Small-cell lung cancer||Platinum-etoposide chemotherapy||Darbepoetin alfa versus placebo||300 μg/weekly for 4 weeks; then every 3 weeks§||≥90 ≤130/140||−11·3 vs. −19·8; P < 0·001||–||–||40 vs. 40 weeks; P = 0·431||Pirker et al (2008)|
Some randomized clinical trials, however, have described decreased overall survival and poorer outcome in cancer patients treated with ESAs (Table III). Henke et al (2003) found that, among 351 patients with head and neck cancer undergoing radiotherapy, those who received Epo had a shorter overall survival. The same group later investigated a subset of 154 patients from this trial to determine whether this adverse effect of Epo was restricted to patients expressing the EpoR (Henke et al, 2006). These patients, in effect, displayed a poorer prognosis in terms of loco-regional progression-free survival compared with the placebo group (P < 0·01), while Epo did not affect the outcome in patients with EpoR-negative tumours. Assessment of this work is rendered problematical by the exceedingly high doses administered (60 000 U/week) and the >150 g/l Hb target reached in most patients, since this may have increased blood viscosity and decreased tissue and tumour oxygenation, and hence rendered radiotherapy less effective.
|No of patients||Malignancy||Treatment||ESA||Dose||Haemoglobin baseline (g/l)||Haemoglobin target (g/l)||Results||Reference|
|351||Head and neck cancer (T3, T4 or node positive)||Radiotherapy||Epoetin beta versus placebo||300 i/u kg−1 × 3 weekly for radiotherapy course||<120 (women) <130 (men)||≥140 (women) ≥150 (men)||Reduced locoregional PFS (HR 1·62; P = 0·0008) Reduced time to locoregional progression (HR 1·69; P = 0·007) Reduced OS (HR 1·39; P = 0·02)||Henke et al (2003)|
|939||Metastatic breast cancer||Chemotherapy||Epoetin alfa versus placebo||40 000–60 000i/u weekly for 12 months||≤130||140||Reduced 12-months OS (70% vs. 76%; P = 0·01)||Leyland-Jones et al (2005)*|
|70||Non-small cell lung cancer (stage III–IV)||Palliative radiotherapy||Epoetin alfa versus placebo||40 000–60 000i/u weekly for 12 weeks||≤120||140||Reduced OS (HR 1·84; P = 0·04)||Wright et al (2007)|
|522||Head and neck cancer (T2–T4 any N)||Radiotherapy||Darbepoetin alfa||150 μg weekly||<140||155||Increased risk of locoregional failure (RR 1·44; P = 0·03); Reduced OS (RR 1·28; P = 0·08)||Overgaard et al (2007)|
|989||Non-myeloid malignancies||None||Darbepoetin alfa versus placebo||6·75 μg/kg every 4 weeks for 16 weeks||<120||130||Reduced OS (HR 1·3 P = 0·022)||Smith et al (2008)|
An equally important question is the specificity of the antibody used for immunohistochemical staining (C-20 anti-EpoR; Santa Cruz Biotechnology, Santa Cruz, CA, USA). Elliott et al (2006) have shown that this antiserum is not suitable for investigating EpoR expression, as it mostly recognizes HSP70 protein, whose levels are increased in tumours and associated with a worse outcome. However, a more recent study by Brown et al (2007) has reported that the specificity of this antibody assessed by immunohistochemistry can be increased by preincubation of C20 with the synthetic peptide HSP70-2, that abolishes non-specific cytoplasmic staining, but retains membranous staining. Additional criticism concerned the imbalance of risk factors in favour of the placebo group (smoking, tumour relapse before treatment, more advanced stage of disease).
Similar evidence of Epo’s adverse impact on overall survival was provided by a study of 939 metastatic breast cancer patients randomized to receive ESAs or placebo for 12 months (Leyland-Jones et al, 2005). This study was terminated early because of a higher mortality in the ESAs arm in the first 4 months of therapy. However, the randomization design of this study had many limitations because of imbalance of risk factors, such as advanced age, lower performance status, greater extent of disease and a higher risk for thromboembolic events. Further biases were the absence of standard assessment and of important prognostic factors, such as definition of disease site, initial prognosis, specific assessment of tumour response at predefined intervals, and type, duration and dose of chemotherapy (Leyland-Jones, 2003).
A randomized, double-blind, placebo-controlled study involving 70 patients (less than a quarter of the designed 300-patient sample) with advanced non-small-cell lung cancer reported decreased overall survival in those treated with epoetin alfa compared with a placebo (63 vs. 129 d; P = 0·04) (Wright et al, 2007), and was also terminated earlier because of concerns raised in other trials, rather than problems encountered in this study. The recent results of the interim analysis of the Danish Head and Neck Cancer study, which comprised 522 patients with head and neck tumours and had, as the primary end point, loco-regional disease control, demonstrated a poorer outcome in patients randomized to receive darbepoetin alfa (Overgaard et al, 2007). In addition, Smith et al (2008) found a shorter survival of subjects treated with darbepoetin alfa after a 2-year follow-up in a randomized placebo-controlled study of 989 patients with various tumour types not receiving chemotherapy or radiotherapy.
Studies on haematological malignancies have also provided conflicting results. A clinical trial found no difference in survival in 344 patients with multiple myeloma, non-Hodgkin lymphoma, Waldenström macroglobulinaemia, Hodgkin lymphoma and chronic lymphocytic leukaemia, treated with darbepoetin alfa versus placebo (Hedenus et al, 2003, 2005). A retrospective study of 257 patients with multiple myeloma has recently demonstrated that ESAs are associated with improved overall survival in anaemic patients at Southwestern Oncology Group stages II, III and IV [hazard ratio (HR) 0·6; 95% confidence interval (CI) = 0·38–0·94] (Baz et al, 2007). In contrast, another retrospective assessment of 323 myeloma patients treated with ESAs and followed up between 1988 and 2007 has shown their shorter survival (31 vs. 67 months; P < 0·001) and median progression-free survival (14 vs. 30 months; P < 0·001) compared to untreated patients (Katodritou et al, 2008). However, this study has important limitations in its design, especially because of baseline differences between the two groups in the most important prognostic factors for multiple myeloma (higher age, higher International Staging System stage, lower platelet count, haemoglobin levels, serum albumin, higher serum creatinine, lactate dehydrogenase and β2-microglobulin in the ESAs group), as well as in disease stage and lines of treatment (Ludwig et al, 2008).
A meta-analysis by Hedenus et al (2005), of four randomized, double-blind, placebo-controlled studies conducted including lymphoproliferative malignancies and solid tumours and evaluating the impact of darbepoetin alfa on progression-free survival and overall survival did not show differences compared to placebo (HR 0·92; 95% CI = 0·78–1·07; and HR 0·95; CI = 0·78–1·16, respectively).
A recent meta-analysis of 19 randomized controlled studies on 2805 patients with various types of cancer (Bohlius et al, 2005) evaluated the impact of ESAs on overall survival. It showed a trend towards improvement of survival with ESAs (HR 0·84, 95% CI = 0·69–1·02). A subsequent update of this analysis, including additional studies (Bohlius et al, 2006), however, has shown a shift towards decreased survival (HR 1·08, 95% CI = 0·99–1·18; 42 trials and 8167 patients) and an increased risk of thromboembolic events (RR 1·67, 95% CI = 1·35–2·06; 35 trials and 6769 patients). It is suggested that this shift may be related to the inclusion of patients with higher baseline and target Hb levels, and greater doses of ESAs.
Lastly, no effect of epoetin beta on survival and tumour progression was found by Aapro et al (2008) in another meta-analysis of 12 randomized controlled studies comprising 2301 patients with solid tumours and non-myeloid haematological tumours. This study assessed the effects on a subgroup of patients with baseline Hb ≤ 110 g/l, whose analysis demonstrated a significant lower risk of progression.
These data, therefore, provide no convincing evidence of the real impact of ESAs on overall survival in cancer patients, nor whether this impact is related to their correction of anaemia or other biological effects. Although these results require further and appropriately designed clinical trials, they indicate that administration of ESAs in anaemic neoplastic patients demands caution, strict observation of guidelines, and evaluation of both the benefits and the acceptability of risk. Indeed, most clinical trials have used a Hb target concentration >120 g/l, higher than presently recommended, and three studies were conducted outside the currently approved indications (after radiotherapy or in anaemic patients not receiving concurrent chemotherapy).
In view of the reports on the safety of ESAs, the American Society of Hematology and the American Society of Clinical Oncology (ASH/ASCO) updated their clinical practice guidelines in 2007 (Rizzo et al, 2008). They recommend the initiation of ESAs treatment at Hb level ≤100 g/l, an Hb target of 120 g/l, and the payment of close attention to thromboembolic complications, including deep venous thrombosis, pulmonary embolism, angina, myocardial infarction, and stroke. There is abundant evidence that ESAs are associated with thrombotic events (Bohlius et al, 2006). A systematic overview from the Cochrane Collaboration and MEDLINE and EMBASE databases comparing ESAs with placebo or standard care in anaemic cancer patients confirmed a higher thromboembolic risk in patients receiving ESAs (7·5% vs. 4·9%; RR 1·57; 95% CI = 1·31–1·87), and an increased mortality risk (HR 1·10; 95% CI = 1·01–1·2) (Bennett et al, 2008). Previous studies in patients with kidney and heart disease (Besarab et al, 1998) had shown that the increased risk of thromboembolic accidents was related to target Hb levels (140 g/l) and haematocrit value (42%). In this patient setting, in fact, when the Hb concentration ranged between 113 and 135 g/l, no increase of thrombotic risk was reported (Singh et al, 2006). Finally, it should be mentioned that this risk is further increased by a prior history of thromboses, surgery, prolonged immobilization or by treatment with thalidomide or lenalidomide in myeloma patients (Bennett et al, 2006).
ESAs have been used worldwide for many years on thousands of anaemic patients with cancer, although there is no definite evidence to date that indicates that their use results in increased survival. However, recent studies are both suggesting extension of their administration for the treatment of cerebral ischaemia or myocardial infarction, and expressing concern about their safety. Given that most randomized studies have various limitations in their design, additional randomized, controlled studies should be exploited with the aim of estimating both benefits and harms of ESAs administration in more homogeneous patient subgroups with chemotherapy-associated anaemia.
The role of EpoR, including its exact structure and expression on normal and cancer cells, requires more appropriate investigations. At variance from erythroid progenitor cells, thus far it has not been conclusively shown that ESAs activate EpoR signalling in tumour cells. As excessively high doses of ESAs have been used to detect cell changes, this cannot be considered as conclusive evidence that the EpoR (if expressed on the cell surface at all) is able to provide signalling at concentrations that can hardly be achieved in a tumour in vivo. In addition, their modulated functions are not clear, given that ESAs do not promote cell proliferation and an anti-apoptotic effect. The tumour progression and reduction of overall survival described in some trials may thus be due to other mechanisms. Future preclinical investigations should specifically address the role of ESAs in cancer biology, possibly with the help of animal models. In addition, clinical studies, carefully designed and properly powered, should assess their effects on crucial issues, such as tumour response, quality of life, progression-free and overall survival.
In our opinion, the potential risk asserted for the use of ESAs should be counterbalanced by the observation that long-term treatment (often more than 20 years in anaemic patients with renal failure) has not provided evidence of an increased risk of tumour development or progression.
This work was supported by a grant from Associazione Italiana per la Ricerca sul Cancro (AIRC), Milan, Italy.
- 2008) Effect of treatment with epoetin-β on survival, tumour progression and thromboembolic events in patients with cancer: an updated meta-analysis of 12 randomised controlled studies including 2301 patients. British Journal of Cancer, 99, 14–22. , & (
- 2001) Erythropoietin and erythropoietin receptor expression in human cancer. Cancer Research, 61, 3561–3565. , , , , , & (
- 2003) Hypoxia-inducible erythropoietin signaling in squamous dysplasia and squamous cell carcinoma of the uterine cervix and its potential role in cervical carcinogenesis and tumor progression. American Journal of Pathology, 162, 1789–1806. , , , , , , , & (
- 2006) Preclinical evaluation of erythropoietin administration in a model of radiation-induced kidney dysfunction. International Journal of Radiation Oncology, Biology, Physics, 64, 1513–1518. , , , , , , , & (
- 2008) The non-haematopoietic biological effects of erythropoietin. British Journal of Haematology, 141, 14–31. (
- 2001) Erythropoietin enhances recovery after cisplatin-induced acute renal failure in the rat. Nephrology, Dialysis, Transplantation, 16, 932–938. , , , , , , , , & (
- 2007) Recombinant human erythropoietin is associated with increased overall survival in patients with multiple myeloma. Acta Haematologica, 117, 162–167. , , , , , , , & (
- 2004) Erythropoietin induces cancer cell resistance to ionizing radiation and to cisplatin. Molecular Cancer Therapy, 3, 1525–1532. , , , , , , & (
- 2006) Thalidomide- and lenalidomide-associated thromboembolism among patients with cancer. Journal of the American Medical Association, 296, 2558–2560. , , , , , & (
- 2008) Venous thromboembolism and mortality associated with recombinant erythropoietin and darbepoetin administration for the treatment of cancer-associated anemia. Journal of the American Medical Association, 299, 914–924. , , , , , , , , , , , , , , , , , , , & (
- 1998) The effects of normal as compared with low hematocrit values in patients with cardiac disease who are receiving hemodialysis and epoetin. New England Journal of Medicine, 339, 584–590. , , , , , , & (
- 2004) Erythropoietin both protects from and reverses experimental diabetic neuropathy. Proceedings of the National Academy of Sciences of the United States of America, 101, 823–828. , , , , , , , , , , , , , & (
- 2006) Protective effect of erythropoietin and its carbamylated derivative in experimental Cisplatin peripheral neurotoxicity. Clinical Cancer Research, 12, 2607–2612. , , , , , , , , , , , , , , & (
- 2001) Activation of the transcription factor NF-kappaB by the erythropoietin receptor: structural requirements and biological significance. Cellular Signalling, 13, 673–681. , , , & (
- 2005) Recombinant human erythropoietin and overall survival in cancer patients: results of a comprehensive meta-analysis. Journal of the National Cancer Institute, 97, 489–498. , , , , , & (
- 2006) Recombinant human erythropoietins and cancer patients: updated meta-analysis of 57 studies including 9353 patients. Journal of the National Cancer Institute, 98, 708–714. , , , , , , , , , , , , , & (
- the Epoetin β QOL Working Group. (2003) Impact of epoetin β on quality of life in patients with malignant disease. British Journal of Cancer, 88, 988–995. , & &
- 2003) Critical role for PI3-kinase in the control of erythropoietin-induced erythroid progenitor proliferation. Blood, 101, 3436–3442. , , , , , , , & (
- 2005) Emerging biological roles for erythropoietin in the nervous system. Nature Reviews Neuroscience, 6, 484–494. & (
- 2004) Erythropoietin mediates tissue protection through an erythropoietin and common beta-subunit heteroreceptor. Proceedings of the National Academy of Sciences of the United States of America, 101, 14907–14912. , , , , , , , , , , , , , , & (
- 2007) Erythropoietin receptor expression in non-small cell lung carcinoma: a question of antibody specificity. Stem Cells, 25, 718–722. , , , , , , & (
- 2003) Recombinant human erythropoietin protects the myocardium from ischemia-reperfusion injury and promotes beneficial remodeling. Proceedings of the National Academy of Sciences of the United States of America, 100, 4802–4806. , , , , , , , & (
- 1995) Recombinant human erythropoietin stimulates angiogenesis in vitro. Kidney International, 47, 740–745. , & (
- 2001) Anemia as an independent prognostic factor for survival in patients with cancer: a systemic, quantitative review. Cancer, 91, 2214–2221. , , & (
- 2005) Weekly epoetin alfa maintains hemoglobin, improves quality of life, and reduces transfusion in breast cancer patients receiving chemotherapy. Journal of Clinical Oncology, 23, 2597–2605. , , , & (
- 1998) The effectiveness and tolerability of epoetin alfa in patients with multiple myeloma refractory to chemotherapy. International Journal of Clinical and Laboratory Research, 28, 127–134. , , , , , , , , , , , , & (
- 2001) Efficacy of epoetin alfa in the treatment of anaemia of multiple myeloma. British Journal of Haematology, 113, 172–179. , & (
- 2001) Erythropoietin-mediated neuroprotection involves cross-talk between Jak2 and NF-kappaB signalling cascades. Nature, 412, 641–647. & (
- 2006) Induction of signalling in non-erythroid cells by pharmacological levels of erythropoietin. Neurodegenerative Diseases, 3, 94–100. , , , & (
- 2007) Impaired downregulation following erythropoietin receptor activation in non-small cell lung carcinoma. Stem Cells, 25, 380–384. , & (
- 2001) The use of epoetin alfa to increase and maintain hemoglobin levels during radiotherapy. Seminars in Oncology, 28(2 suppl. 8), 42–48. (
- 1999) Regulation of the erythropoietin gene. Blood, 94, 1864–1877. & (
- 2002) Erythropoietin therapy for acute stroke is both safe and beneficial. Molecular Medicine, 8, 495–505. , , , , , , , , , , , , , , , , , , , , , & (
- 2006) Anti-Epo receptor antibodies do not predict Epo receptor expression. Blood, 107, 1892–1895. , , , , , , , , & (
- 2004) Oxygen-dependent and tissue-specific regulation of erythropoietin gene expression. The American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, 286, R977–R988. (
- 2006) Erythopoietin stimulates growth and STAT5 phosphorylation in human prostate epithelial and prostate cancer cells. Prostate, 66, 135–145. , , , , & (
- 2007) Erythropoietin protects cardiac myocytes against anthracycline-induced apoptosis. Biochemical and Biophysical Research Communications, 354, 372–378. & (
- 2009) Constitutively active erythropoietin receptor expression in breast cancer cells promotes cellular proliferation and migration through a MAP-kinase dependent pathway. Biochemical and Biophysical Research Communications, 379, 696–701. , & (
- 2005) Efficacy and safety analysis of epoetin alfa in patients with small-cell lung cancer: a randomized, double-blind, placebo-controlled trial. Journal of Clinical Oncology, 23, 9377–9386. , , , , , , , & (
- 1996) Signal transduction of erythropoietin in endothelial cells. Kidney International, 50, 481–488. , , , , & (
- 2008) Erythropoietin stimulates cancer cell migration and activates RhoA protein through a mitogen-activated protein kinase/extracellular signal-regulated kinase-dependent mechanism. Journal of Pharmacological Experimental Therapy, 324, 1227–1233. & (
- 2006) Erythropoietin improves myocardial performance in doxorubicin-induced cardiomyopathy. European Heart Journal, 27, 1876–1883. , , , , , & (
- 2005) Human recombinant erythropoietin (rEpo) has no effect on tumour growth or angiogenesis. British Journal of Cancer, 93, 1350–1355. , , , , , , & (
- 2006) Erythropoietin biology in cancer. Clinical Cancer Research, 12, 332–339. , , , & (
- 2007) Erythropoietin blockade inhibits the induction of tumor angiogenesis and progression. PLoS ONE, 2, e549. , , , , , , , & (
- 2003) A novel role for erythropoietin during fibrin-induced wound-healing response. American Journal of Pathology, 163, 993–1000. , , & (
- 2002) Impact of tumor hypoxia and anemia on radiation therapy outcomes. The Oncologist, 7, 492–508. , , , & (
- 2003) Darbepoetin alfa 20000161 Study Group. Efficacy and safety of darbepoetin alfa in anaemic patients with lymphoproliferative malignancies: a randomized, double-blind, placebo-controlled study. British Journal of Haematology, 122, 394–403. , , , , , , , , , , , , & (
- 2005) Darbepoetin alfa for the treatment of chemotherapy-induced anemia: disease progression and survival analysis from four randomized, double-blind, placebo-controlled trials. Journal of Clinical Oncology, 23, 6941–6948. , , , & (
- 2003) Erythropoietin is a potent physiologic stimulus for endothelial progenitor cell mobilization. Blood, 102, 1340–1346. , , , , , , , , & (
- 2003) Erythropoietin to treat head and neck cancer patients with anaemia undergoing radiotherapy: randomised, double-blind, placebo-controlled trial. Lancet, 362, 1255–1260. , , , , , , , , , & (
- 2006) Do erythropoietin receptors on cancer cells explain unexpected clinical findings? Journal of Clinical Oncology, 24, 4708–4713. , , , , , & (
- 2002) A new high affinity binding site for suppressor of cytokine signaling-3 on the erythropoietin receptor. European Journal of Biochemistry, 269, 2516–2526. , , , & (
- 2008) Characterization of erythropoietin receptor and erythropoietin expression and function in human ovarian cancer cells. International Journal of Cancer, 122, 274–280. , , , & (
- 1993) The effect of recombinant human erythropoietin treatment on tumour radiosensitivity and cancer-associated anaemia in the mouse. British Journal of Cancer, 68, 720–726. , , , & (
- 2008) Erythropoiesis-stimulating agents are associated with reduced survival in patients with multiple myeloma. American Journal of Hematology, 83, 697–701. , , , , , , , , & (
- 2005) Brain-derived erythropoietin protects from focal cerebral ischemia by dual activation of ERK-1/-2 and Akt pathways. FASEB Journal, 19, 2026–2028. , , , , & (
- 1997) The role of tyrosine phosphorylation in proliferation and maturation of erythroid progenitor cells – signals emanating from the erythropoietin receptor. European Journal of Biochemistry, 249, 637–647. (
- 1995) Specific recruitment of SH-PTP1 to the erythropoietin receptor causes inactivation of JAK2 and termination of proliferative signals. Cell, 80, 729–738. , , , & (
- 2007) Expression of erythropoietin receptor and in vitro functional effects of epoetins in B-cell malignancies. Clinical Cancer Research, 13, 3536–3544. , , , , , , , & (
- 2006) Erythropoietin activates the phosphoinositide 3-kinase/Akt pathway in human melanoma cells. Melanoma Research, 16, 275–283. , , , & (
- 2005) Erythropoietin-mediated activation of JAK-STAT signaling contributes to cellular invasion in head and neck squamous cell carcinoma. Oncogene, 24, 4442–4449. , , , , , , & (
- 2006) Recombinant epoetins do not stimulate tumor growth in erythropoietin receptor-positive breast carcinoma models. Molecular Cancer Therapy, 5, 347–355. , , , , , , & (
- 2005) Attenuation of interstitial inflammation and fibrosis by recombinant human erythropoietin in chronic cyclosporine nephropathy. American Journal of Nephrology, 25, 64–76. , , , , , , , , & (
- 2005) Erythropoietin promotes MCF-7 breast cancer cell migration by an ERK/mitogen-activated protein kinase-dependent pathway and is primarily responsible for the increase in migration observed in hypoxia. Journal of Biological Chemistry, 280, 39273–39277. , , & (
- BEST investigators and Study Group. (2003) Breast cancer trial with erythropoietin terminated unexpectedly. Lancet Oncology, 4, 459–460. (Comment in: Lancet Oncology 2004; 5, 206–207)
- 2005) Maintaining normal hemoglobin levels with epoetin alfa in mainly nonanemic patients with metastatic breast cancer receiving first-line chemotherapy: a survival study. Journal of Clinical Oncology, 23, 5960–5972. , , , , , , , , , , , , , & (
- 2007) Erythropoietin reduces cisplatin-induced apoptosis in renal carcinoma cells via a PKC dependent pathway. Cancer Biological Therapy, 6, 1944–1950. , , & (
- 2006) A single bolus of a long-acting erythropoietin analogue darbepoetin alfa in patients with acute myocardial infarction: a randomized feasibility and safety study. Cardiovascular Drugs and Therapy, 20, 135–141. , , , , , , , , , & (
- 2001) Effects of epoetin alfa on hematologic parameters and quality of life in cancer patients receiving nonplatinum chemotherapy: results of a randomized, double-blind, placebo-controlled trial. Journal of Clinical Oncology, 19, 2865–2874. , , , & (
- 2004) Effect of haemopoietic growth factors on cancer cell lines and their role in chemosensitivity. Oncogene, 23, 981–990. , , , , & (
- 2006) Intrinsic and extrinsic erythropoietin enhances neuroprotection against ischemia and reperfusion injury in vitro. Journal of Neurochemistry, 96, 1101–1110. , , , & (
- 2007) Do cancer cells express functional erythropoietin receptors? New England Journal of Medicine, 356, 2447. (
- 2004) The European Cancer Anaemia Survey (ECAS): a large, multinational, prospective survey defining the prevalence, incidence, and treatment of anaemia in cancer patients. European Journal of Cancer, 40, 2293–2306. , , , , , , , , , , & (
- 2008) ESAs not the culprit: more studies required. American Journal of Hematology, 83, 880. , , , , & (
- 2005) CERA (Continuous Erythropoietin Receptor Activator): a new erythropoiesis-stimulating agent for the treatment of anemia. Current Hematology Reports, 4, 436–440. (
- 2005) Erythropoietin induces neovascularization and improves cardiac function in rats with heart failure after myocardial infarction. Journal of the American College of Cardiology, 46, 125–133. , , , , , , , & (
- 2006) Erythropoietin protects sensory axons against paclitaxel-induced distal degeneration. Neurobiology of Disease, 24, 525–530. , , , & (
- 2006) Signals for stress erythropoiesis are integrated via an erythropoietin receptor-phosphotyrosine-343-Stat5 axis. Journal of Clinical Investigation, 116, 683–694. , , , , & (
- 2001) Erythropoietin induces tumor regression and antitumor immune responses in murine myeloma models. Proceedings of the National Academy of Sciences of the United States of America, 98, 5181–5186. , , , & (
- 2004) Erythropoietin has an anti-myeloma effect – a hypothesis based on a clinical observation supported by animal studies. European Journal of Haematology, 72, 155–165. , , , , , & (
- 2005) Erythropoietin signaling promotes invasiveness of human head and neck squamous cell carcinoma. Neoplasia, 7, 537–543. , , , , , & (
- 2005) Cardioprotection by recombinant human erythropoietin following acute experimental myocardial infarction: dose response and therapeutic window. Cardiovascular Drugs and Therapy, 19, 243–250. , , , & (
- 2005) Impact of epoetin-β on survival of patients with lymphoproliferative malignancies: long-term follow up of a large randomized study. British Journal of Haematology, 129, 206–209. , & (
- 2007) Preclinical studies of erythropoietin receptor expression in tumour cells: impact on clinical use of erythropoietic proteins to correct cancer-related anaemia. European Journal of Cancer, 43, 510–519. , , , , & (
- 2007) Randomized study of the importance of novel erythropoiesis stimulating protein (Aranesp) for the effect of radiotherapy in patients with primary squamous cell carcinoma of the head and neck (HNSCC): the Danish Head and Neck Cancer Group DAHANCA 10 rand. European Journal of Cancer, Suppl, 5, 7. , & (
- 2008) Safety and efficacy of darbepoetin alpha in previously untreated extensive-stage small-cell lung cancer treated with platinum plus etoposide. Journal of Clinical Oncology, 26, 2342–2349. , , , , , & (
- 2006) Erythropoietin treatment in advanced multiple myeloma is associated with improved immunological functions: could it be beneficial in early disease? British Journal of Haematology, 135, 660–672. , , , , , , & (
- 2006) Double-blind, placebo-controlled study of quality of life, hematologic end points, and safety of weekly epoetin alfa in children with cancer receiving myelosuppressive chemotherapy. Journal of Clinical Oncology, 24, 3583–3589. , , , , , & (
- 1999) Human erythropoietin induces a pro-angiogenic phenotype in cultured endothelial cells and stimulates neovascularization in vivo. Blood, 93, 2627–2636. , , , , , , , & (
- 2008) Use of epoetin and darbepoetin in patients with cancer: 2007 American Society of Hematology/American Society of Clinical Oncology clinical practice guideline update. Blood, 111, 25–41. , , , , , , , , , , , & (
- 1998) In vivo evidence that erythropoietin protects neurons from ischemic damage. Proceedings of the National Academy of Sciences of the United States of America, 95, 4635–4640. , , , , , & (
- 2000) CIS3/SOCS-3 suppresses erythropoietin (EPO) signaling by binding the EPO receptor and JAK2. Journal of Biological Chemistry, 275, 29338–29347. , , , , & (
- 2005) Effects of early intervention with epoetin alfa on transfusion requirement, hemoglobin level and survival during platinum-based chemotherapy: results of a multicenter randomised controlled trial. European Journal of Cancer, 41, 1560–1569. , , , , , & (
- 2006) Erythropoietin in experimental acute renal failure. Nephron. Experimental Nephrology, 104, e83–e88. & (
- 2001) The negative impact of anemia on radiotherapy and chemoradiation outcomes. Seminars in Hematology, 38(Suppl. 7), 8–15. (
- 1996) A constitutively activated chimeric cytokine receptor confers factor-independent growth in hematopoietic cell lines. Blood, 88, 455–464. , , & (
- 1999) Effects of recombinant human erythropoietin on the antitumor effect of cisplatin in SCID mice bearing human ovarian cancer: a possible oxygen effect. Gynecologic Oncology, 73, 280–284. & (
- 2005) Erythropoietin in heart failure. Seminars in Nephrology, 25, 397–403. , , , , , & (
- 2007) Expression and function of erythropoietin receptors in tumors: implications for the use of erythropoiesis-stimulating agents in cancer patients. Cancer, 110, 477–488. , , , , & (
- 2008) Erythropoietin receptor transcription is neither elevated nor predictive of surface expression in human tumour cells. British Journal of Cancer, 98, 1059–1067. , , , , , , , , , & (
- 2006) Correction of anemia with epoetin alfa in chronic kidney disease. New England Journal of Medicine, 355, 2085–2098. , , , , , & (
- 2008) Darbepoetin alpha for the treatment of anemia in patients with active cancer not receiving chemotherapy or radiotherapy: results of a phase III, multicenter, randomized, double-blind, placebo-controlled study. Journal of Clinical Oncology, 26, 1040–1050. , , , , , , , & (
- 1994) Recombinant human erythropoietin and the anemia of cancer. Blood, 84, 997–1004. (
- 2008) Effects of anemia correction with epoetin beta in patients receiving radiochemotherapy for advanced cervical cancer. International Journal of Gynecological Cancer, 18, 515–524. , , , , , & (
- 2001) Recombinant human erythropoietin increases the radiosensitivity of xenografted human tumours in anaemic nude mice. Journal of Cancer Research and Clinical Oncology, 127, 346–350. , , , , & (
- 1998) Enhanced radiosensitivity in experimental tumours following erythropoietin treatment of chemotherapy-induced anaemia. British Journal of Cancer, 78, 752–756. , , , & (
- 2001) Erythropoietin restores the anemia-induced reduction in cyclophosphamide cytotoxicity in rat tumors. Cancer Research, 61, 1358–1361. , & (
- 1999) The erythropoietin receptor. International Journal of Biochemistry and Cell Biology, 31, 1001–1005. & (
- 2008) Local erythropoietin signaling enhances regeneration in peripheral axons. Neuroscience, 154, 767–783. , , , , , , , & (
- 2003) Erythropoietin protects cardiac myocytes from hypoxia-induced apoptosis through an Akt-dependent pathway. Biochemical and Biophysical Research Communications, 308, 990–994. , , , , , , , & (
- 2006) Antiapoptotic effects of erythropoietin in differentiated neuroblastoma SH-SY5Y cells require activation of both the STAT-5 and AKT signaling pathways. Journal of Biological Chemistry, 281, 5648–5656. & (
- 2007) A “classical” homodimeric erythropoietin receptor is essential for the antiapoptotic effects of erythropoietin on differentiated neuroblastoma SH-SY5Y and pheochromocytoma PC-12 cells. Cellular Signalling, 19, 634–645. , & (
- 2002) Double-blind, placebo-controlled, randomized phase III trial of darbepoetin alfa in lung cancer patients receiving chemotherapy. Journal of the National Cancer Institute, 94, 1211–1220. , , , , , , , , , & (
- 2005) Erythropoietin as a retinal angiogenic factor in proliferative diabetic retinopathy. New England Journal of Medicine, 353, 782–792. , , , , , , , , , , , , , & (
- 2000) Erythropoietin stimulates proliferation of human renal carcinoma cells. Kidney International, 58, 647–657. & (
- 2006) Epoetin alfa in platinum-treated ovarian cancer patients: results of a multinational, multicentre, randomised trial. British Journal of Cancer, 94, 947–954. , , , & for the EPO-INT-45 Study Group. (
- 2005) Phase III, randomized, double-blind study of epoetin alfa compared with placebo in anemic patients receiving chemotherapy. Journal of Clinical Oncology, 23, 2606–2617. , , , , , , , , , & (
- 2007) Erythropoietin is neuroprotective on GABAergic neurons against kainic acid-excitotoxicity in the rat spinal cell cultures. Brain Research, 1154, 31–39. , , , , & (
- 2007) Randomized, double-blind, placebo-controlled trial of erythropoietin in non-small-cell lung cancer with disease-related anemia. Journal of Clinical Oncology, 25, 1027–1032. , , , , , , , , , , , & (
- 1998) Estrogen-dependent production of erythropoietin in uterus and its implication in uterine angiogenesis. Journal of Biological Chemistry, 273, 25381–25387. , , , , & (
- 2001) Inhibition of erythropoietin signalling destroys xenografts of ovarian and uterine cancers in nude mice. British Journal of Cancer, 84, 836–843. , , , , , , , , , & (
- 2003) Erythropoietin regulates tumour growth of human malignancies. Carcinogenesis, 24, 1021–1029. , , , , , , , , , , , , & (
- 2002) Erythropoietin receptor signalling is required for normal brain development. Development, 129, 505–516. , , , , , , , , , , & (